The monitor of the pattern and dynamics of molecular genetic variation in free-ranging populations has revealed much about the factors that influence population nd species survival. Using the methods of molecular genetics (allozyme, two dimensional electrophoresis, restriction fragment length polymorphism of nuclear and mitochondrial DNA, and polymerase chain reaction) to monitor sequence variation), we have discovered several components that influence stability of natural populations. Historic inbreeding has been deduced in endangered populations of cheetahs, lions, Florida panthers and black-footed ferrets. The consequences of these inbreeding events included inbreeding depression as reflected in congenital defects and physiological impairment to reproduction. Further, as inbreeding reduces genetic diversity, these events increase susceptibility and vulnerability of populations to infectious disease vectors that occasionally evolve mechanisms to abrogate immune differences. Finally, efficacious application of the molecular clock hypothesis has resolved divergence timing and phylogenetic placement of species of orangutan, giant panda, and other species of carnivores and primates.